Figure: (a) Real part of complex permittivity and (b) Dielectric loss tangent of LLDPE-nano-MgSiO₃ composites.

Team members: Pulin Dutta and Kunal Borah.

DOI: https://doi.org/10.1007/s11664-022-09775-5

The main concern for electronic devices with the development of modern electronic industries is substrates with specific properties for high-frequency applications. The key factors that determine the capability of a material to be used in high-frequency microwave devices are its complex permittivity and complex permeability. Since a single material may not always be able to meet all the requirements for a specific application, composites such as a polymer matrix with inclusions of various types (Nano, ceramic, magnetic etc.) could be a good choice. Dielectric ceramics have good dielectric strength, low dielectric constant and low loss tangent, which ensure that composites of polymer-dielectric ceramic nano-materials can be potential substrate materials for different types of microwave applications. 

In this work dielectric property of magnesium silicate (MgSiO₃) and linear low-density polyethylene nano-composite are studied in the X-band frequencies to realize its application as a substrate for high-frequency devices. MgSiO₃ ceramics are synthesized by conventional solid state technique. Structural and morphological characteristics of MgSiO₃ nanoparticles are confirmed by X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. Transmission electron microscopy images reveal the average particle size to be ~100 nm. Composites are prepared by uniform dispersion of the nano-inclusions MgSiO₃ in a linear low-density polyethylene matrix in three different wt.%, viz. 2%, 4% and 6%. The fractured lateral side of the composite is examined under a scanning electron microscope to ensure the uniform dispersion of the inclusions in the polymer. Water absorption measurement is carried out based on ASTM D570-98. From the water absorption graph it is seen that the saturation for all the samples are obtained after 168 h of immersion. Densities of the samples are measured by hydrostatic weighing by using Archimedes principle. From the studies it is seen that the percentage of water absorption increases with increase in inclusion content. This is due to the moderately high water absorption properties of the inclusion as compared to the LLDPE matrix. Thermal conductivity of the composites is measured by modified hot plat method. In this studies also, the value of thermal conductivity increases with increase in inclusion content. Nicolson-Ross approach is used to investigate the dielectric characteristics of the composites. The permittivity and dielectric loss tangent of the nano-composite in the X-band are found to be ~2.2–2.5 and 10⁻²–10⁻⁴ for all the inclusion concentration respectively. The complex permittivity shows a linear trend with minimal variation, which is due to the accumulation of space charge at the inclusion-polymer interfaces. As per the investigation, the composite can be utilized as Microstrip patch antenna (MPA) substrate, which is further confirmed by the calculated RL values. The complex permittivity and dielectric loss tangent results established in this work also fulfill the International Technology Roadmap for Semiconductors (ITRS) criteria for substrate materials.

This work has been published in the Journal of Electronic Materials. Furthermore, different types of unused materials such as silicates e.g. alumino silicates and liquid crystals e.g. 5O.4, 6O.4 can be synthesized to use as an inclusion in polymer matrix for MPA substrates. Also, for performance enhancement one can choose other available polymer matrix, e.g. HDPE, LDPE, PDMS, PVA etc.